[Bug other/42333] complex division failure on darwin10 with -lm

[dominiq at lps dot ens dot fr]

------- Comment #11 from dominiq at lps dot ens dot fr  2009-12-08 22:13 -------
I think I understand why apple gcc42 does not show the problem: it does not
call ___divdc3:

[macbook] f90/bug% diff -up pr42333_42.s pr42333_45.s
--- pr42333_42.s        2009-12-08 23:00:29.000000000 +0100
+++ pr42333_45.s        2009-12-08 23:00:07.000000000 +0100
...
@@ -15,68 +15,61 @@ LCFI2:
        movq    %rax, -16(%rbp)
        movabsq $9214364837600034815, %rax
        movq    %rax, -8(%rbp)
-       movq    -16(%rbp), %rax
-       movq    -8(%rbp), %rdx
-       movq    %rax, -24(%rbp)
-       movsd   -24(%rbp), %xmm1
+       movq    -16(%rbp), %rdx
+       movq    -8(%rbp), %rax
        movq    %rdx, -24(%rbp)
        movsd   -24(%rbp), %xmm0
-       movapd  %xmm0, %xmm2
-       addsd   %xmm1, %xmm2
-       movapd  %xmm0, %xmm3
-       subsd   %xmm1, %xmm3
-       movsd   LC1(%rip), %xmm0
-       movapd  %xmm2, %xmm1
-       divsd   %xmm0, %xmm1
-       movsd   LC1(%rip), %xmm0
-       movapd  %xmm3, %xmm2
-       divsd   %xmm0, %xmm2
-       movapd  %xmm2, %xmm0
-       movsd   %xmm1, -24(%rbp)
-       movq    -24(%rbp), %rax
+       movq    %rax, -24(%rbp)
+       movsd   -24(%rbp), %xmm1
+       movsd   LC2(%rip), %xmm3
+       movsd   LC2(%rip), %xmm2
+       call    ___divdc3
        movsd   %xmm0, -24(%rbp)
        movq    -24(%rbp), %rdx
...

This also explain why the test compiled with -c and 4.5, but linked with 4.2
fails. So my guess about the lazy complex division seems right in libm. Could
someone write a C code forcing the use of ___divdc3?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42333